A typical, commercially available, prior art hydraulic BOP, incorporated into a conventional production wellhead tree, is illustrated in FIG. 1. It will be noted that the assembly involves:
a BOP housing which forms opposed horizontal ram chambers and has threaded side connections, the BOP housing further having threaded top and bottom connections for connecting with other components of the production wellhead; PA1 the BOP housing also forms a vertical central fluid production bore extending therethrough and the ram chambers extend between the external surface of the housing and the bore; PA1 the ram chambers each contain a sealed ram comprising an inner elastomeric element and an outer, steel body; PA1 a pair of external housings are connected to the side connections; and PA1 each external housing forms an internal space or chamber which contains a sealed piston which supports a return spring--the piston is connected with the ram and a port is formed in the external housing outer end wall, for connection with a hydraulic line; PA1 whereby hydraulic fluid, supplied under pressure to the external housing through the hydraulic line, advances the piston to drive the ram into the wellhead bore to assume a closed position for sealing around a rod string (not shown) and the return spring retracts the ram and piston to an open position when the hydraulic pressure is released. PA1 a bottom connection adapted to connect and seal with a tubing head; PA1 a BOP housing, whose side wall forms opposed side openings or chambers for containing BOP rams, which chambers communicate or connect with the fluid production bore--it will be noted that the chambers can be described as being `buried` in the side wall; PA1 a flow tee housing forming a side opening communicating with the bore and having means for connecting with a flow line; and PA1 a top connection for sealing and connecting with the next component of the production wellhead, usually a stuffing box. PA1 an integral production wellhead tree having a BOP housing; PA1 the side wall of the BOP housing forming a pair of horizontal opposed chambers, each extending between the housing's external surface and the tree's vertical bore; PA1 the side wall of the tree forming a first passageway means, extending between the tree's external surface and the outer end of each chamber, through which hydraulic fluid may be supplied under pressure; PA1 preferably a BOP ram and piston assembly is positioned within each chamber; PA1 whereby hydraulic fluid may be supplied through the first passageway means to the chambers to bias the ram and piston assemblies to a closed position; PA1 a pair of external housings is disengagably secured to the BOP housing side wall for closing and sealing the outer ends of the chambers; PA1 each external housing preferably forms a sealed internal space or chamber; PA1 preferably a shaft element is connected with each ram and piston assembly and extends into the internal space of the associated external housing; and PA1 return means, such as a spring, are preferably provided in each external housing internal space, for acting on the shaft element to bias the ram and piston assembly to the open position. PA1 that the BOP ram and piston are provided as assemblies which are wholly located within the housing chambers; PA1 that the chambers and the hydraulic fluid passageway (which both must contain pressure) are buried within the tree side wall; and PA1 that the external housings do not necessarily have to be constructed so as to contain pressure.
It will be noted that the external housings form the hydraulic chambers for the BOP and must be fluid tight and of sturdy enough structure to contain the hydraulic pressure.
In a recent development, an integral production wellhead tree was disclosed in Canadian Patent No. 2,197,584, (the "'584 patent"), issued to the present applicant. This tree, shown in FIG. 2, involves integrating BOP and flow tee housings between top and bottom tubing head connections, as a unitary steel body. More particularly the tree comprises a forged or cast one-piece body forming a vertical fluid production bore and incorporates:
The tree of the '584 patent further has a generally cylindrical configuration, which results in a relatively thick side wall when compared with prior production wellheads.